Kirchner was a hugely prolific artist, with thousands of artworks still in existence even despite the best efforts of the ruling Third Reich to destroy as many as they could. Amongst his sketch work remains around 20,000, at the best guess, in a variety of forms of completeness. Some would be artworks in their own right, others would be in preparation for a painting or sculpture. Many of this huge collection are to be found in bound sketchbooks, some of which occasionally come up for sale at auction. A recent estimate of £150,000 - £200,000 was placed on a single sketchbook from the artist, which contained a total of 40 pieces from cover to cover. That would give a crude estimate of up to £5,000 per each individual drawing.
Many artists have found that sketchbooks have offered a portable way to capture scenes on the go, wherever their travels may take them. Most famously, William Turner would quickly put together scenes of landscapes across Europe in his small books before expanding upon them within his own studio, perhaps as a larger-scale oil painting or watercolour. Claude Monet would learn from that and do similar. Kirchner followed these same principles, though many of his drawings were actually figurative and also within his own uniquely Expressionist style.
Some quotes that have been uncovered about his career have explained just exactly how hard working and passioniate he was, and any artist would not be able to carry canvases and painting equipment with them wherever they went - this medium was the next best option. To underline just how connected he was this art form, on a daily basis, would be that a small book was actually found in his possession on the day of his passing. Whilst sadness is felt regarding the troubles that he experienced within his lifetime, he still was able to achieve so much that truly the overwhelming feeling should be of celebration at his brilliance and also that his reputation remains strong in the present day.
The German artist built up such a huge collection of work that he would often happily gift away selections of his paintings and drawings. His spell in photography also left behind thousands of negatives which would become harder and harder to store away safely and securely, whilst still accurately documented. Many of his skecthbooks were essentially just artistic diaries, where he would also place artworks alongside his thoughts of the day, even shopping lists. The key focus would always be his artistic experimentations. Close friends would sometimes be given collections of these drawings and as most of them were highly knowledgeable about art, and Kirchner's career more specifically, they would be delighted to receive personal items such as these.